Heretofore, plastic composites reinforced with glass fibers and carbon fibers have been known in the art and have found extensive utility in various applications. The strength of such composites is greatly increased by the presence of reinforcing fibers and by the interfacial strength between the fibers and the plastic matrix. This interfacial strength is directly proportional to the contact surface area between the fibers and the plastic matrix. Addition to the contact surface area necessitates an increase in the aspect ratio of the fibers. The aspect ratio is the ratio of length to diameter of the fibers. The diameter of these fibers, however, can only be reduced so far. Thus, the amount that the interfacial strength can be increased by increasing the aspect ratio is also limited. The practice of reinforcing the plastic composites by incorporating fibers therein in an interwoven form has been popular even though it complicates the process of production.
In recent years, aromatic polyamides, generically called Alamides, have been developed as rigid polymers and have found utility as reinforcing fibers. Since these aromatic polyamides exhibit poor adhesiveness to other resins, the aromatic polyamide fibers must be provided with improved adhesive properties to be used effectively in the plastic composites.
Japanese Patent Application Disclosure SHO 57(1982)-195,136 discloses an ionomeric resin composition reinforced with aromatic polyamide fibers, the composition comprising 40 to 99.9 parts by weight of an olefinic ionomeric polymer and 60 to 0.1 parts by weight of para-oriented wholly aromatic polyamide fibers. The aromatic polyamide fibers are formed of repeating units represented by the general formulas, --NH--Ar.sub.1 NH--CO--Ar.sub.2 --CO-- and/or --NH--Ar.sub.3 --CO-- wherein Ar.sub.1, Ar.sub.2, and Ar.sub.3 stand for different para-oriented aromatic groups, and the surface thereof is modified by N-substitution. Examples of the N-substituent groups include alkyls, aralkyls, hydroxyalkyls, and carboxylates. The introduction of the N-substituent enables the wholly aromatic polyamide fibers to acquire improved dispersibility in the ionomeric resin and improved adhesiveness thereto. The introduction of the substituent nevertheless impairs the strength of the wholly aromatic polyamide fibers. Moreover, since the reinforcing material is fibrous, its aspect ratio cannot be substantially increased and it can only reinforce the composites to a limited extent.
In view of the above mentioned limitations of using fibers to increase the strength of plastics, a polymer blend type composite (molecular composite) having the so-called mutual immersion type structure has been produced. The structure is obtained by causing the so-called rigid polymer such as the aromatic polyamide to be dispersed so finely in a flexible matrix polymer as to reach the molecular level. Since the molecular composite of the nature just mentioned is unaffected by the principle that strength is produced by unidirectional orientation of molecular chains of the rigid polymer, it exhibits little anisotropy and has excellent physical properties such as mechanical strength, thermal stability, and resistance to solvents.
U.S. Pat. No. 4,207,407 discloses a polymeric alloy which is comprised of a coil-shaped heterocyclic polymer and a rigid aromatic heterocyclic polymer represented by the following formulas: ##STR1##
These polymers are dissolved in methanesulfonic acid solvent and the polymeric solution obtained is cast on a surface, treated to remove the solvent, and then dried to give rise to the polymeric alloy. When this polymeric alloy is used for structural materials in aircraft and automobiles, for example, the physical properties of the polymer alloy are degraded and the metallic members of the aircraft or automobiles placed in contact with the polymer alloy are corroded due to the extremely corrosive solvent used to produce the alloy.